apex:message

A message for a specific component, such as a warning or error. If an <apex:message> or <apex:messages> component is not included in a page, most warning and error messages are only shown in the debug log.

Example

<!-- For this example to render properly, you must associate the Visualforce page
with a valid account record in the URL.
For example, if 001D000000IRt53 is the account ID, the resulting URL should be:
https://Salesforce_instance/apex/myPage?id=001D000000IRt53
See the Visualforce Developer's Guide Quick Start Tutorial for more information. -->